The present invention relates to electronic memory devices and more particularly to circuitry for securing an electronic memory from piracy of the data stored in it.
A digital signal processor is a high speed microcomputer usable for applications requiring digitally adaptive, secure, and intelligent signal processing. Such processors may be used to accomplish pattern recognition, adaptive control storage, intelligent finite impulse filtering, linear circuit control, encryption, diagnostics, precision servo control, voice band data processing and many other applications. They find use, for example, in industrial robots to synthesize and recognize speech, sense objects with radar or optical intelligence and perform mechanical operations through digital servo loop computations. They are also used in direct broadcast satellite systems for implementing encryption algorithms.
Processors of this type include an internal memory which stores data. This data comprises both program instructions and constants. The data may include certain proprietary information which must be protected from unauthorized access and alteration.
The present invention relates to a digital signal processor called DSP320EE12, which shares many features of the DSP320C10, a commercially available device produced by Microchip Technology Incorporated, Chandler, Ariz. However, the DSP320EE12 also includes an improved internal program memory in the form of an integrated electronically erasable and programmable read only memory (EEPROM) with a 2.5K word (40K bits) capacity and an expanded internal data RAM (static) with a 256 word (4K bits) capacity.
Although the DSP320EE12 uses EEPROM, the concept of providing an internal security for program memory is more generic and is applicable to other erasable internal program memories such as EPROM, RAM and NVRAM. Also, although the DSP320EE12 is a digital signal processor, the concepts of this invention are applicable to any processor with on chip memory.
The improved processor has a unique addressing system which is disclosed in copending application Ser. No. 191,983, filed May 9, 1988 and entitled "Method And Apparatus For Controlling The Movement Of Data In A RAM Of A Digital Signal Processor." The improved digital signal processor also has the capability of programming the internal EEPROM at the same time as a program is being executed, as described in copending application Ser. No. 191,984, filed May 9, 1988, entitled "Digiital Signal Processor With Run Time Programming Capability." The reader is referred to those applications for further details of those aspects of the processor.